1. Field of the Invention
The present invention relates to screening apparatus for use at an overflow weir in a sewerage system and a method of manufacturing screening apparatus. More specifically, the screening apparatus is configured for use with a side weir of a sewerage channel.
2. Description of the Related Art
Sewerage channels carry a mixture of liquids and solids to treatment plants. During wet weather, some channels receive rain water and consequently their flow levels are raised. To manage increased flow rates, such channels are provided with overflow weirs which allow excess water to leave the sewerage system and enter a watercourse such as a river.
In order to prevent undesirable solids from leaving the sewerage channel by the overflow weir and entering a watercourse, it is known to provide a screen along the weir. Such a screen allows a flow of water over the weir but screens out solid matter which is maintained in the flow in the sewerage channel.
A screen in this situation can become blinded, i.e. blocked, by the solid matter in the mixture. Consequently, it is known to provide screens in the form of a horizontal continuous moving band which move past a cleaning device to prevent blinding. During high flow level conditions, the lower surfaces of the screen provide the filtering function while the upper surface is intended to operate above the water level such that it may be cleaned by the brush.
Such screens are limited in their effectiveness to allow water to flow freely over the weir. In addition, during extreme conditions, the brush may become submerged which leads to ineffective cleaning and the screen becoming rapidly blinded. Consequently, the screen becomes completely ineffective until the extreme conditions have subsided.
U.S. Pat. No. 4,242,205 to Hirs discloses a continuous belt filter having a horizontal portion and a portion at an upward angle to the horizontal. The top of the angled portion is positioned such that in normal use it is not submerged in the liquid to be filtered. The non-submerged portion is provided with a water or air jet for cleaning. This design is not believed to be suitable for use in a sewerage system.
Accordingly, it is an object of the present invention to provide a screen apparatus for use at an overflow weir in a sewerage system that can be cleaned effectively even when water is flowing over the weir.